Conventional methods for manufacturing hollow, revolute components from composite materials typically require extensive tooling fixtures and labour-intensive assembly procedures. One such method involves wrapping carbon fibres around a rotating mandrel which provides the basic shape of the component. The carbon fibres are pre-impregnated with a thermoset epoxy resin, and are applied over the rotating mandrel in multiple plies to form the hollow component.
Filament winding, fibre placement, and tape laying are three known methods for applying composite fibres to a rotating mandrel to form a hollow component. In a filament winding process, the mandrel is typically suspended horizontally between end supports. The mandrel rotates about the horizontal axis as a fibre application instrument moves back and forth along the length of the mandrel, placing fibres onto the mandrel in a pre-determined configuration. In most applications, the filament winding apparatus passes the fibre material through a resin bath just before the material touches the mandrel. This is called wet winding. In other applications, often termed dry winding, the fibre has been pre-impregnated with resin, eliminating the need for the resin bath. Following oven or autoclave curing of the resin, the mandrel can remain in place and become part of the wound component, or it can be removed.
Tape laying is similar to the fibre placement process described above except that fibre tape, rather than individual fibre tows, is laid down on the rotating mandrel to form the hollow component. Narrower tape widths provide enhanced steerability and control during application and are often used for the production of hollow components having a non-cylindrical shape.
A problem with this type of component forming is that the geometry of the component is limited by the need to be able to remove the mandrel from the finished cured component. Thus, for example, components having a double curved form, such as a convergent-divergent nozzle cannot be formed without the use of multi-piece mandrels. This can cause joint discontinuities which in turn can be difficult and costly to rectify.
A further problem with conventional tooling is that a separate mandrel must be manufactured for each component form and size. Conventional mandrels are generally formed as ring roll forged metal components which make their production costly and time-consuming. In addition, the need for separate mandrels for each component form and size, results in the need to store large quantities of mandrels which is inconvenient.
Furthermore, the expansion and contraction of the mandrels during the heating cycle portion of the curing process (involving temperatures of ≈135° C.) results in conventional mandrels having a finite useful working life. This may be as little as 100 cycles, before replacement of the mandrel is required.